Transcript for Z-Pak Could Lead to Death for Those With Heart Conditions, Says FDA

And tonight we want to bring you a medical alert about a very popular antibiotic, z-pak, the fda says the drug could lead to sudden death for some people, who have certain heart conditions. Which ones? Abc's chief medical editor, dr. Richard besser tells us more about the medicine andn to be concerned. Reporter: It's prescribed nearly 60 million times a year to treat common infections -- ear, nose, throat and chest. So popular, people ask for it by name. Do you v have a patient with a coal or flu who says, doc, give me a z-pak? All the time. Reporter: But today, that warning from the fda. Also known as zithromax or azith row micin, can cause abnormal changes in the electrical activity of the heart, which can be fatal. Tonight pfizer tells abc news they're updating their labels with that abc warning, listing those conditions. Many patients may not know they have those conditions and too often people ask for z-pak when they start to feel sick. R have you asked for z-pak? Yes. Reporter: Z-pak is safe for most people. But to reduce your risk, know your family's heart history and your own, but the best advice, don't request antibiotics, they only work for some infections. We want to be the heroes, make people feel happy and better. Reporter: But remember, antibiotics won't make you feel better if you only have a cold or the flu. Dr. Richard besser, abc news, new york.

This transcript has been automatically generated and may not be 100% accurate.

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